Generally, a vehicular brake is a mechanical device for retarding the motion of the vehicle by means of friction. These brakes use friction between brake surfaces that turn with the wheels and friction pads that are stationary with respect to the turning wheels to convert the kinetic energy of the moving vehicle into heat. There are tremendous forces involved in braking a vehicle, and these forces can result in the generation of considerable heat during braking, as well as the wear of the friction surfaces and pads of the brakes. Wear may be accelerated by, among other things, dirt or dust that may infiltrate the brake assembly and migrate to locations between the pads and the friction surfaces. In addition, because the friction pads in use today are no longer made with asbestos, a superior heat-dissipating material, accelerated wear due to the effects of high heat generation is more common than in the past.
Vehicles are generally equipped with drum-type or disc-type brakes. Most vehicles in use today are provided with disc-type brakes on at least the front wheels, and sometimes on all four wheels. Drum-type brakes were more commonly used in the past than they are today, but they are still utilized on the rear wheels of a significant number of vehicles.
Disc-type brakes operate by forcing friction pads (brake linings) against both sides of a rotating disc-shaped rotor. This rotor turns with the wheel of the vehicle and within a stationary housing called the caliper assembly. When the brakes are applied, hydraulic fluid causes pistons in the caliper assembly to push the friction pads against the rotating disc-shaped rotor, thereby retarding the motion of the vehicle.
The rotor is generally comprised of a pair of annular metal discs joined together by a plurality of spacers that are arranged so as to maximize the heat-dissipating area of the annular discs. The annular discs are supported by a central end wall which is disposed generally parallel to the discs. This end wall, which is typically joined to the discs by a short connecting sidewall, generally has a central hole to accommodate the spindle on which the associated wheel is mounted, and a plurality of bolt holes to accommodate the lug bolts or studs that are used to mount the wheel to the vehicle. Early rotors of disc-type brake systems were provided with a hub or raised collar around the central hole in the end wall. More recently, however, hubless rotors have been used, which are characterized by a substantially flat end wall. Many hubless rotors are of a unitary construction, wherein the end wall, adjacent sidewall and one of the annular discs are formed from a single piece of metal. Other hubless rotors are of a composite construction, wherein the end wall and adjacent sidewall are formed from a separate, usually considerably thinner, piece of metal from those which form the annular discs.
Drum-type brakes include a metal brake drum which rotates with the wheel. The drum has an internal cylindrical friction surface against which brake shoes, equipped with friction pads (brake linings), having arcuate external surfaces that correspond to the internal surface of the drum, are pushed by the action of a piston.
A brake drum is comprised of an end wall, around which is disposed a depending sidewall, the internal surface of which serves as the friction surface. This end wall generally has a central hole to accommodate the spindle on which the associated wheel is mounted, and a plurality of bolt holes to accommodate the lug bolts or studs that are used to mount the wheel to the vehicle. Early brake drums were provided with a hub or raised collar around the central hole in the end wall. More recently, however, hubless drums have been used, which are characterized by a substantially flat end wall. Some hubless drums, like rotors, are of a unitary construction, wherein the end wall and the adjacent sidewall are formed from a single piece of metal. Most hubless drums, however, are of a composite construction, wherein the end wall is formed from a separate, usually considerably thinner, piece of metal from that which forms the adjacent sidewall.
Brake drums and rotors can vary considerably in size, depending primarily on the size and weight of the vehicle that they must stop. The center hole sizes in the end walls of the drums and rotors can also vary in size, to accommodate spindles of various sizes. Typically, the larger and heavier the vehicle, the larger the drum or rotor and spindle, and the larger the center hole in the end wall of the drum or rotor. In recent years, so-called "super-duty" braking systems have been developed for busses and large trucks. The drums and rotors of such super-duty systems are correspondingly larger and heavier than the drums and rotors of passenger cars and light trucks, and they are generally of unitary construction. Although the outside diameter of hubless brake drums and rotors can vary across a considerable range, such workpieces will typically have end wall center hole diameters that vary within a range of about 2.50 inches to about 5.75 inches.
Wear, misuse or improper maintenance of brake drums and rotors can lead to damage, such as warping or the development of grooves or scoring in the friction surfaces. Such surface damage will reduce the effectiveness of the brakes by reducing the areas of such surfaces that are placed into contact with the friction pads to slow the vehicle. Warping, grooves and scoring in worn brake discs and drums may generally be removed, however, if not too deep or extensive, to restore full function to the brakes. Since rotors and drums have a significant value, refacing of the friction surfaces is economically preferably to replacement, if it can be accomplished at a reasonable cost.
A brake rotor or drum is generally removed from the vehicle and mounted on a lathe to machine or reface its friction surface or surfaces. Typically, a lathe for machining brake drums and rotors is equipped with a rotating shaft, sometimes referred to as a spindle or an arbor, on which the workpiece may be mounted, and a slide assembly on which a cutting or grinding tool may be mounted. Generally, the shaft has a threaded portion at its outer end, which shaft is insertable through the central hole in the end wall of a brake drum or rotor in order to facilitate mounting of such workpiece thereon. As the workpiece is turned on the shaft, the cutting or grinding tool is advanced, either automatically or manually, into engagement with the workpiece to trim or shave metal therefrom until the desired dimension and surface finish are obtained.
It is essential that the workpiece be mounted in a secure fashion on the lathe so that the end wall of the workpiece may be maintained in a position substantially perpendicular to the axis of rotation of the shaft while the workpiece is being machined. This will insure that the friction surface or surfaces of the workpiece will be maintained in an unvarying position relative to the cutting or grinding tool as the workpiece is rotated on the shaft, so that machining of the friction surface or surfaces may produce a smooth finish. However, since brake drums and rotors are provided in a variety of sizes to fit a variety of cars and other vehicles, the end walls of such workpieces may vary in diameter and thickness, and the central hole therein may also vary in diameter. Therefore, it is also desirable that the lathe mounting system for such workpieces possess some flexibility or adaptability to permit the mounting of workpieces having different physical configurations. Unfortunately, however, existing mounting systems have generally failed to combine security in mounting with adaptability to permit the mounting of workpieces of different types and configurations. Most of the mounting systems that permit the mounting of differently sized workpieces achieve this adaptability through a use of many components, each of which is adapted for a particular drum or rotor configuration. Such systems, requiring a large number of components in order to accommodate various configurations, are frequently too expensive for the small brake shop operator to justify.
It has been common practice to mount a workpiece on a lathe by securing it between or against one or more cones. The use of cones offers some flexibility in dealing with various center hole configurations, and it also permits the workpiece to be readily centered with respect to the central hole in its end wall. A workpiece having a hub around its central hole is typically mounted between two cones, each having a cylindrical bore therethrough, that are slidably mounted on the shaft of the lathe with the smaller ends thereof facing together and protruding into opposite sides of the hub. A hubless drum or rotor is frequently mounted using a single such cone that is employed in combination with other components. Typically, the cone is placed on the shaft with its smaller end facing the workpiece, and this smaller end of the cone is inserted into the central hole of the workpiece. A backing component may also be employed on the side of the workpiece opposite the cone, so that the workpiece will be held between the cone and the backing component. Thus, the cone and its backing component cooperate with the central hole in the end wall of the workpiece to align and hold the workpiece on the lathe.
An example of such a mounting system is described in U.S. Pat. No. 4,708,041 of Granger. The system of Granger employs a cone having a cylindrical bore therethrough, which cone is adapted to slide over a cylindrical tubular component having an enlarged cylindrical termination at one end thereof. This component, which Granger refers to as a roto-hub, also has a hollow cylindrical recess having a square cross-section within its termination at the junction of the cylindrical termination and the tubular portion. The roto-hub is mounted on the shaft of a lathe, and the drum or rotor to be machined is placed thereover. The cone, which has a small end and a large end, is then slid over the cylindrical tubular portion of the roto-hub so that its small end is received within the cylindrical recess in the cylindrical termination. However, the workpiece is secured on the shaft only by friction between the inside surface of the cone and the outside surface of the tubular portion of the roto-hub.
A similar mounting system to that of Granger, but one that is specifically designed for use in connection with hubless drums and unitary hubless rotors, is manufactured and sold by RELS Manufacturing Company of Rockford, Minn. This system is designed to fit over the arbor or shaft of a lathe. It includes a center locator comprising a substantially cylindrical tube portion having an enlarged cylindrical terminal member at one end. The center locator has a central bore that is adapted to receive the shaft in sliding engagement therewith, and the axis of the central bore is substantially coincident with the axis of the tube portion of the center locator. The tube portion has an outside diameter that is smaller than the diameter of the central hole in the end wall of the drum or rotor, and the terminal member of the locator is larger than said central hole. The system also includes a cone having a large base end and a smaller opposite end and a central bore therethrough such that the axis of the central bore is substantially coincident with the axis of the cone, said bore being adapted to receive the tube portion of the center locator in sliding engagement therewith. The cone has a diameter at its base end that is larger than the diameter of the central hole in the end wall of the drum or rotor. The terminal member also has a beveled surface extending radially outwardly from its junction with the cylindrical tube portion of the center locator. This beveled surface is disposed at an angle similar to that of the conical surface of the cone, so that the workpiece may be positioned over the center locator and the cone may be positioned over the tube portion of the center locator, with its smaller end preceding its base end and protruding through the central hole in the end wall of the workpiece to engagement with the beveled surface of the terminal member. A spacer may be placed over the cylindrical tube portion of the center locator, if necessary, and a nut is threaded over external threads on the outer end of the locator to hold the assembly in place. Similar or identical systems are made and sold by several manufacturers besides RELS, but for simplicity, a system of this type will be referred to herein as the RELS system. One advantage of the RELS system over the system of Granger is the fact that the nut of the RELS system more securely holds the cone in place against the end wall of the workpiece than does the frictional engagement between the cone and the roto-hub of Granger.
The use of a cone and an associated backing member such as is employed by the Granger system or the RELS system for hubless drums and rotors may not prevent vibration of the workpiece as it is machined, because in such a system, all of the force that is applied to hold the workpiece securely is applied in the vicinity of the central hole. When the cutting or grinding tool is applied to the friction surface or surfaces of a workpiece held by such a system, the forces applied by the tool in a direction parallel to the axis of rotation at a point some distance away from the central hole may be sufficient to cause deflection or vibration in the workpiece. This deflection or vibration will be more pronounced in workpieces of composite construction, having thinner end walls than workpieces of unitary construction, and in fact such composite workpieces may be distorted or deformed under the influence of such forces. In addition, deflection or vibration in the workpiece, sometimes referred to as "chattering", precludes obtaining a smooth finish on the friction surface or surfaces. Consequently, it has sometimes been considered advantageous to provide an additional stabilizing force on the end wall of the workpiece itself in order to hold it securely with respect to the cutting or grinding tool.
One mounting system that provides such additional stabilizing force on the end wall of the workpiece was especially developed for use in connection with composite rotors by RELS Manufacturing Company of Rockford, Minn. This system employs a pair of circular plates instead of a cone and backing plate to hold the workpiece on the shaft. The RELS system for composite rotors also utilizes the center locator and the nut and spacer of the RELS system for drums that is discussed hereinabove. However, instead of using a cone to align and hold the rotor on the locator, this system uses a pair of plates, each of which is provided with a central hole that is adapted for sliding engagement with the center locator. One of the plates is substantially flat, and the other has a raised ring around its central hole. This ring is precisely sized to fit inside and to mate with the central hole in a particular rotor. Since each such plate has two sides or faces, one raised ring may be provided on each side, but each such plate can then only accommodate rotors having two specific center hole sizes. It would be necessary to have a plurality of such plates in order to be prepared to machine rotors having different center hole sizes.
Another means for providing an addition al stabilizing force on the end wall of the workpiece is described in U.S. Pat. No. 4,165,662 of Besenbruch et al. The Besenbruch system has two embodiments, one for holding a drum and one for holding a rotor. In order to mount a drum, the Besenbruch system employs as a backing member an adapter having a front face with a conical recess and a central hole therethrough so that the adapter may be fit over the shaft of the lathe. After this adapter and the drum are placed over the shaft, a cone having a cylindrical bore and a small end and a large end is fitted over the shaft so that its small end protrudes through the central hole in the end wall of the drum and is received in the adapter. A circular, rigid, anti-chatter, aligning and straightening plate having a central hole to receive the shaft is then placed over the shaft in front of the drum. The plate is provided with a plurality of threaded holes spaced therearound to receive a plurality of adjustment bolts, which bear adjustably against the circular end wall of the drum. The shaft has a threaded hole in its end, and a bolt is provided that mates with the threaded hole. A plurality of spacers are placed over the bolt and the bolt is threaded into the end of the shaft.
The Besenbruch system for rotors includes a pair of cones, each having a cylindrical bore and a small end and a large end, as well as a cylindrical adapter having a central bore and a conical end face. One cone is fitted over the shaft so that its small end faces outwardly. The cylindrical adapter is then placed over the shaft so that the small end of the first cone protrudes into its central bore, and the rotor is placed in front of the adapter. The second cone is then placed over the shaft so that its small end protrudes through the central hole in the end wall of the rotor and is received in the cylindrical adapter. A circular, rigid, anti-chatter, aligning and straightening plate that is essentially identical to the one employed for drums is then placed over the shaft in front of the drum. The plate, like the one for drums, is provided with a plurality of threaded holes spaced therearound to receive a plurality of adjustment bolts, which bear adjustably against the circular end wall of the rotor. The shaft has a threaded hole in its end, and a bolt is provided that mates with the threaded hole. A plurality of spacers are placed over the bolt and the bolt is threaded into the end of the shaft. When either of the Besenbruch systems are installed to hold a workpiece on a lathe, the various adjustment bolts must each be adjusted to apply a stabilizing force to the end wall of the workpiece in order for the anti-chatter plate to be effective. Furthermore, it is frequently necessary to adjust the bolts, turn the workpiece on the lathe to check for vibration and adjust the bolts again to eliminate it. Several adjustment steps may be required before machining of the workpiece can proceed.
Another means for providing a stabilizing force on the end wall of a workpiece was devised primarily for use in connection with workpieces of unitary construction, having relatively thick end walls. This mounting means employs a cone that is placed on the shaft with its small end protruding into the central hole of the end wall of the workpiece, and a pair of bell-shaped clamps that are placed on the shaft with their open "bell" ends facing the end wall, one on each side. A spring may also be placed between one of the bell clamps and the cone to maintain the cone in place in contact with the central hole in the end wall of the workpiece. Suitable spacers are placed over the shaft outside the outer bell clamp and a nut is fastened onto the externally-threaded outer end of the shaft. The bell clamps are thereby secured in place on the shaft, each in contact with one side of the end wall of the workpiece, although generally, the configuration of the "bell" ends is such that only a part thereof will be in contact with the end wall.
This mean s of mounting a workpiece on the rotary shaft of a lathe may be acceptable for use in mounting many brake drums and rotors of unitary construction, because it applies a stabilizing force at several widely separated points on the end wall. However, such mounting means may not be suitable for use with the newer drums and rotors of composite construction. As has been mentioned, the thinner end walls of composite drums and rotors are more likely to be subject to vibration and deflection during machining than are the thicker end walls of workpieces of unitary construction. Therefore, the bell clamps generally do not apply sufficient force on the thin end walls of composite workpieces to maintain them in a stable position with respect to the cutting or grinding tool. Consequently, the workpieces will be subject to vibration or chattering, which precludes obtaining a smooth finish on the friction surface or surfaces.
In order to eliminate vibration and chattering in the end walls of composite drums and rotors, it is necessary to apply a greater force to the end walls than can readily be applied by the bell clamps, without causing distortion of the shaft. As has been mentioned, the bell clamps were designed to provide a stabilizing force or forces to the end wall of a workpiece. They were not designed to provide a larger force, a clamping or compressive force, such as is generally required to prevent or eliminate chattering. One reason that the bell clamps do not provide sufficient force to hold the end walls is that they are fastened in place by means of a nut that is threaded onto the externally-threaded outer end of the arbor or shaft. This arbor is generally designed so that the nut on its threaded end may be used to hold a workpiece or an adapter in place thereon, but it is not generally suitable for the application of compressive forces to items mounted thereon. If it is desired to tighten the nut so as to apply a compressive force thereby, care must be taken to avoid overtightening that warps the end of the shaft so that it is no longer properly aligned with its axis of rotation. Another reason that the bell clamps do not provide sufficient compressive force to hold the thin end walls is due to the wide spacing of the stabilizing forces which they apply to the end wall. As has been mentioned, the bell clamps generally have gaps in their contact surfaces, or the surfaces that contact the end wall of the workpiece. These gaps are designed to reduce the surface area in contact with the end wall so that the minimal force applicable through the tightening of the arbor nut will be translated into a sufficient force per unit area that will serve to stabilize the workpiece on the arbor. However, this stabilizing force is generally not sufficient to prevent vibration and chattering in workpieces having thin end walls as such workpieces are machined. In addition, this stabilizing force is frequently inadequate to hold the workpiece securely so as to prevent it from slipping as its friction surface or surfaces are machined on the shaft.
It would be desirable, therefore, if a kit of components could be developed that would be suitable for securing a workpieces comprising brake drums and rotors of unitary or composite construction on a lathe having a rotary driven shaft, such that the end wall of the workpiece is maintained in a position substantially perpendicular to the axis of rotation of the shaft. It would also be desirable if such a kit could be developed that would be suitable for mounting workpieces having a variety of end wall sizes and thicknesses, and having a variety of central hole sizes, without requiring a separate adapter for each of the various sizes and end wall configurations. It would also be desirable if such a kit could be developed that would be suitable for mounting both drums and rotors in the same or a similar fashion. It would also be desirable if such a kit could be developed that is capable of applying a compressive force to the end wall of a workpiece, especially one of composite construction, in order to eliminate vibration without the risk of warping the shaft of the lathe. It would also be desirable if such a kit could be developed that would not require that several adjustment steps be taken to eliminate chattering in the end wall of the workpiece. It would also be desirable if such a kit could be developed that would be compatible with existing systems for mounting of workpieces.